Steps in evaluation

Step one: verify tachycardia and hemodynamic stability. If unstable refer to ACLS algorithms please. 

Step two: determine whether the QRS is narrow complex or wide complex

Step three: if narrow complex determine whether irregular or regular rhythm

Step four: if wide complex tachycardia, determine whether monomorphic or polymorphic

Algorithm for the initial ECG review and differential diagnosis of tachycardia

ECG: electrocardiogram; AVNRT: atrioventricular nodal reentrant tachycardia; AVRT: atrioventricular reciprocating (bypass-tract mediated) tachycardia; AT: atrial tachycardia; SANRT: sinoatrial nodal reentrant tachycardia; AF: atrial fibrillation; AV: atrioventricular; VT: ventricular tachycardia; SVT: supraventricular tachycardia; WPW: Wolff-Parkinson-White.
* A narrow QRS complex is <120 milliseconds in duration, whereas a wide QRS complex is ≥120 milliseconds in duration.
¶ Refer to UpToDate topic reviews for additional details on specific ECG findings and management of individual arrhythmias.
Δ Monomorphic VT accounts for 80% of wide QRS complex tachycardias; refer to UpToDate topic on diagnosis of wide QRS complex tachycardias for additional information on discriminating VT from SVT.

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Algorithm for the evaluation of narrow QRS complex tachycardia in stable patients